A digital still camera is representative of cameras for recording video images on a random-accessible recording medium. In a dominant configuration of the digital still cameras, both one still picture image and additional information of the still picture image are recorded as one file in a memory card.
The following advantage can be provided by this configuration in which both one still picture image and additional information of the still picture image are recorded as one file. That is, when a camera is connected to a personal computer through a digital interface such as a USB and accessed as a drive from the personal computer, file handling is made more convenient. Suppose that a still picture image and additional information of the still picture image are recorded as two separate files. For example, when copying a plurality of still picture images, the number of files to be copied is doubled compared with the case where the still picture image and the additional information are recorded as one file. Similarly, when deleting a plurality of still picture images, the number of files to be deleted is doubled. Thus, when a still picture image and additional information of the still picture image are recorded as one file, file handling on a personal computer is made easier.
Additional information to be recorded by the digital still camera includes attribute information such as a shooting date and time, and a thumbnail image of 160 by 120 pixels. In each file, the additional information is arranged ahead of a still picture image. Further, since the additional information as well as the still picture image is inserted in a format complying with a JPEG standard, the whole file also complies with the JPEG standard.
Meanwhile, a camera referred to as a disk movie is an example of cameras for recording moving pictures on a random-accessible recording medium. In the disk movie, a moving picture is recorded in a format of an MPEG transport stream on an optical disk, and additional information is recorded ahead of an area in which the moving picture has been recorded, so that the moving picture and the additional information can be handled as one file.
According to an MPEG standard, a video stream (video data) and an audio stream (audio data) are divided into packets in units of 188 bytes, and each packet is referred to as a transport packet. Further, a mixed arrangement of a video transport packet and an audio transport packet is referred to as an MPEG transport stream.
Additional information with respect to a video image can be stored, for example, in a private stream (private data) according to the MPEG standard, which is one of structures for storing self data. The private stream is divided into packets in units of 188 bytes to create transport packets, and the transport packets are arranged ahead of a transport stream of a moving picture. A transport stream with the additional information arranged at the front thus can be configured.
FIG. 7 shows a packet structure of a moving picture file in a conventional disk camera. In FIG. 7, a P_TSP represents a transport packet of a private stream containing additional information. Further, a V_TSP and an A_TSP represent a transport packet of a video stream and a transport packet of an audio stream, respectively. The V_TSPs and the A_TSPs are configured in the order defined in the MPEG standard and arranged. Further, a N_TSP represents a null transport packet containing no meaningful information. Further, a PAT and a PMT represent a transport packet containing a Program Association Table and a transport packet containing a Program Map Table, respectively. These two packets are essential in an MPEG transport stream.
These types of transport packets are discriminated from each other by a PID number arranged in a transport packet header portion as shown in FIG. 8. Further, in a payload portion following the transport packet header portion, the private stream, the video stream, or the audio stream is arranged.
FIG. 9 shows an example of a data structure in which the additional information is composed of attribute information such as a shooting date and time, and five thumbnail images. A plurality of the null transport packets, i.e. the N_TSPs, are arranged between the additional information and moving picture information. These N_TSPs need to be arranged so that when the additional information has a data size that is not a multiple of 94 kbytes, compliance with the rules defined in a UDF standard that will be described later is attained, and continuity of the transport packets is secured. In order to meet these two conditions, it is necessary to arrange the N_TSPs continuously until the last byte (188th byte) of the N_TSP and the last byte (2,048th byte) of 2 kbytes coincide with each other for the first time.
Accordingly, one continuous chunk of the N_TSPs has a minimum length of 0 byte and a maximum length obtained by subtracting 188 bytes from 94 kbytes (94 by 1,024 bytes), which is the lowest common multiple of 188 bytes and 2,048 bytes. In actual recording, the length of additional information determines the length of one continuous chunk of the N_TSPs.
FIG. 10 is a block diagram showing the configuration of a conventional disk camera. As shown in FIG. 10, in recording, signals input from a video signal input part 1001 and an audio signal input part 1002 are compressed in a video compressing part 1003 and an audio compressing part 1004, respectively. Based on the video signal and the audio signal that have been compressed, a transport stream assembling part 1005 creates a video and audio transport stream in which the V_TSPs and the A_TSPs are configured in the order defined in the MPEG standard. The created video and audio transport stream is transmitted via a recording part 1006 and a pickup 1007 and written on a phase change optical disk 1008. In reproduction, the video and audio transport stream extracted via the pickup 1007 and a reproducing part 1009 is separated into a video signal and an audio signal in a transport stream disassembling part 1010. The video signal and the audio signal that are obtained by the separation are expanded in a video expanding part 1011 and an audio expanding part 1012, respectively. Then, the video signal and the audio signal are output to a video displaying part 1013 and an audio output part 1014, respectively.
A recording controlling part 1015 creates, in each recording operation by a user, one moving picture file complying with a UDF (Universal Disk Format Specification, Optical Storage Technology Association) file system regarding transport stream structures on the phase change optical disk 1008. Further, the recording controlling part 1015 manages a status of use of a recording area in units of a 2-kbyte logical sector.
A reproduction controlling part 1016 controls operations such as the continuous reproduction of a plurality of files.
A thumbnail image generating part 1017 extracts one field of video signals at 1-minute intervals, subjects the video signals to JPEG compression, and stores the result of the compression in memory.
FIG. 11 shows how one file is managed using the UDF file system as an example. The file is composed of an FID (File Identification Descriptor), a file entry, and file actual data. Address information of the file entry is referred to from an ICB (Information Control Block) column of the FID. The file actual data is composed of an area A (additional information+N_TSPs) and an area B (moving picture information). Allocation descriptors A and B in the file entry refer to the area A (additional information+N_TSPs) and the area B (moving picture information), respectively. Thereby, the two areas A and B are managed as one file. The UDF standard defines an effective data size of the area A (additional information+N_TSPs) as an integer multiple of a logical sector size. As for the area B including an end portion of the file, an effective data size is defined as arbitrary.
FIG. 12 is a flow chart showing the recording procedure of a disk camera in one shooting operation.
Initially, according to a recording starting operation by a user, the recording controlling part 1015 searches for the logical sector area B that can be used in the phase change optical disk 1008 (FIG. 10) and allows moving picture information to be recorded from a leading position of the area B (S1201). Further, in parallel with the recording of the moving picture information on the phase change optical disk 1008, at 1-minute intervals, a thumbnail image of 160 by 120 pixels is stored in a memory housed in the thumbnail image generating part 1017 (FIG. 10) (S1202). The thumbnail image corresponds to a variable data size portion of additional information, which changes in length with shooting time, and attribute information such as a shooting date and time corresponds to a fixed data size portion of the additional information.
For example, when shooting is finished in about 5 minutes, an area is detected that allows recording of additional information composed of attribute information such as a shooting date and time, and five thumbnail images, and the N_TSPs to be added behind the additional information (S1203). Then, the additional information is recorded in the area A (S1204). After that, a chunk of the N_TSPs having a sufficient length is added just behind the additional information (S1205).
Next, in the file entry, the allocation descriptor A (FIG. 11) is set to refer to the additional information and the N_TSPs, and the allocation descriptor B is set to refer to the moving picture information. The file entry thus is created, and the FID (FIG. 11) that refers to the file entry also is created (S1206). In this manner, the procedure of creating one file on the phase change optical disk 1008 is finished (S1207).
In the procedure, the thumbnail images included in the additional information are changed in size to 160 by 120 pixels, for example, by reducing a given field of a video image.
Furthermore, the additional information is used to refer to data stored in a VR_MANGR.IFO that is a file dedicated to additional information according to a video recording standard ver. 1.0 (September 1999) regarding DVD-RAMs. The additional information further is used to refer to Exif Attribute Information stored in an APP1 of a JPEG file according to an Exif standard ver. 2.1 regarding digital still cameras.
Moreover, a method also has been devised, in which additional information of a plurality of files is collected physically and arranged in a given recording area so as to be read collectively at a time, thereby reducing read time with respect to the additional information of the plurality of files. For example, when retrieving additional information with respect to a plurality of files, with additional information arranged collectively, a retrieving operation can be started by collectively reading an area in which the additional information is arranged without a seeking operation performed by a pickup.
In a conventional recording method employing a data structure shown in FIG. 9, a useless area including meaningless data is required, which is composed of the N_TSPs and has a maximum length of about 94 kbytes and an average length of 47 kbytes. Therefore, for example, supposing that 100 moving picture files of about 48 seconds on an average are created at a recording rate of 1.5 Mbps on an optical disk having a recording capacity of 1 Gbytes, it is necessary to create the N_TSPs having a total length of 9.4 Mbytes maximum. That is, an area accounting for 1% of a total recording capacity of the optical disk becomes useless.